The information recording density of magnetic recording systems has been increasing steadily, and the size of a magnetic recording mark per bit has been becoming smaller and smaller. So far, the recording bit size in the magnetic recording system has been mainly reduced by reducing the size of a magnetic recording head and magnetic particles used for a magnetic recording medium. However, since the magnetic recording density exceeded 1 Tbit/inch2, there has been a concern that the magnetic information recorded on the magnetic recording medium may be lost at room temperature due to an influence of thermal fluctuation. To prevent this, a coercive force of the magnetic recording medium needs to be increased. Unfortunately, the magnitude of the magnetic field that can be generated by the magnetic recording head is limited. If the coercive force is excessively increased, the recording bit cannot be formed in the medium. In order to solve this, a thermally assisted magnetic recording method has received attention these days in which at an instant of recording, the medium is heated to reduce the coercive force of the medium, thereby enabling recording on a highly coercive medium. As the thermally assisted magnetic recording method, a method for achieving a high recording density has been heretofore proposed in which a fine light spot with high power density is outputted to a medium to locally heat only a recording region.
Usually, a lens is used to produce the fine light spot. Recently, the distance between the magnetic head and the magnetic recording medium is not more than 10 nm. If a magnetic head is increased in weight due to an optical element such as the lens mounted on the magnetic head, the weight causes problems such as bringing a magnetic recording head into contact with the magnetic recording medium, or hindering air-bearing of the head. Moreover, a plurality of magnetic recording media (disks) are stacked in the magnetic recording apparatus, and an interval between the magnetic recording media is usually not more than 1 mm. For this reason, all the parts provided around the magnetic head have to be accommodated within the height of not more than 1 mm. Accordingly, it is not preferable that the optical element such as the lens be mounted on the magnetic head.
In this regard, in one of method proposed as a method for producing a fine light spot on a magnetic recording medium without using a lens or the like, an optical waveguide including a core and a clad is formed. This method can be implemented by forming a core, by using a material with a large refractive index difference delta-n from the clad, the core having a width and a thickness in the submicron order.